The present invention relates to definition and detection of unusual waveforms acquired by a digital oscilloscope, and more particularly to characterizing newly acquired waveforms for identification of waveform anomalies.
In analog oscilloscopes employing cathode ray tubes (CRTs) for display, variable brightness of the screen display communicates useful information about the activity of the signal being observed. As an analog oscilloscope generates vertical excursions during a horizontal sweep interval to provide a real-time picture of the signal activity at the probe tip, it inherently tends to vary the brightness of the display as an inverse function of the slope of the line it produces.
One feature of an analog oscilloscope or a digital oscilloscope with a high waveform throughput is the ability to detect an intermittent signal anomaly that occurs in an otherwise repetitive signal. Analog oscilloscopes show a faint trace indicating the presence of this intermittent anomalous signal behavior. Of course, if the signal becomes too intermittent, the trace is so faint in brightness that it may be missed entirely by the oscilloscope operator.
U.S. Pat. No. 6,163,758 (Sullivan, et al.), entitled Detection of Unusual Waveforms and assigned to the same assignee as the present invention, discloses an arrangement for detecting unusual waveforms where waveforms are highly repetitive by counting the number of new pixels that are drawn on a screen display, and for generating an alert signal if the number of new pixels exceeds a threshold value. New pixels are defined as those pixels that have never been previously touched by any waveform since the beginning of the present acquisition series, or as those pixels which have not been affected for some interval of time as measured by the decay of values stored in a raster memory. The hardware consists of a single counter and threshold for detecting a significant number of new pixels, and a software algorithm dynamically computes the threshold value. However this presents a rather simplistic characterization of the unusual waveform.
What is desired is a method of characterizing newly acquired waveforms for identifying waveform anomalies based on the variability of a newly acquired waveform from one or more previously acquired waveforms.